Light-emitting polymer composition and organic EL display device using the same

ABSTRACT

A light-emitting polymer composition for a light-emitting layer in an organic EL display device includes at least first and second light-emitting polymers having different interfacial characteristics which lower a cohesion between elements of the first and second light-emitting polymers.

CROSS REFERENCE

This application is a continuation of prior U.S. patent application Ser.No. 10/172,001, filed on Jun. 17, 2002 now U.S. Pat. No. 7,482,066,which claims the benefit of Korean Application No. 2001-66880, filed onOct. 29, 2001, both of which are hereby incorporated by reference forall purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting polymer compositionand an organic electroluminescent (EL) display device using the same.

2. Description of the Related Art

An organic EL display device includes an anode, a hole injection layer,a hole transportation layer, a light-emitting layer, an electrontransporting layer, an electron injection layer, and a cathode, whichare sequentially stacked on a substrate.

The above-described layers of the organic EL display device are made ofa low-molecular organic material or a high-molecular organic material(i.e., a polymer). The layers of the organic EL display devicecomprising a low-molecular organic material are formed by, for example,a vacuum deposition technique, while the layers of the organic ELdisplay comprising a high-molecular organic material are formed by, forexample, a spin coating technique.

In general, an organic EL display device having a light-emitting layerof one color made of a high-molecular organic material is easy tomanufacture and is lower in driving voltage than that of a low-molecularorganic material. However, an organic EL display device having alight-emitting layer of one color made of the high-molecular organicmaterial is lower in light-emitting efficiency and shorter in life spanthan that of the low-molecular organic material.

On the other hand, in forming a light-emitting layer of a full color, anorganic EL display device having the high-molecular organic material hasdifficulties in patterning red, green and blue light-emitting layersusing an ink jet technique or a laser transfer technique, leading to alow light-emitting efficiency and a short life span.

Conventional light-emitting polymer materials are patterned by theink-jet technique or the laser transfer technique. However, in mostcases, light-emitting polymer materials are not transferred using thelaser transfer technique, which is a kind of a thermal transfertechnique.

The thermal transfer technique requires at least a light source, atransfer film, and a substrate. Light emitted from the light source isabsorbed into a light absorbing layer of the transfer film and thenconverted into heat energy. An image forming material of the transferfilm is transferred to the substrate by the heat energy, thereby forminga desired image on the substrate. The thermal transfer technique is alsoused to form a color filter of a liquid crystal display (LCD) device.

FIG. 1 shows a schematic view illustrating a laser transfer operationfor patterning a light-emitting layer of a conventional organic ELdisplay device.

Referring to FIG. 1, an organic film S₂ is formed on a substrate S₁. Alaser beam is irradiated to the substrate S₁ to separate the organicfilm S₂ from the substrate S₁ and transfer it to a substrate S₃.

Here, parameters that determine a transfer characteristic include anadhesion W₁₂ between the substrate S₁ and the organic film S₂, acohesion W₂₂ between elements of the organic films S₂, and an adhesionW₂₃ between the organic film S₂ and the substrate S₃.

The adhesion W₁₂ and W₂₃ and the cohesion W₂₂ can be described by asurface tension and an interfacial tension as follows:W ₁₂=γ₁+γ₂−γ₁₂;W ₂₂=2γ₂₂; andW ₂₃=γ₂+γ₃−γ₂₃,

where γ₁ denotes a surface tension of the substrate S₁, γ₂ denotes asurface tension of the organic film S₂, γ₃ denotes a surface tension ofthe substrate S₃, γ₁₂ denotes an interfacial tension between thesubstrate S₁ and the substrate S₂, γ₂₂ denotes an interfacial tensionbetween the elements of the organic film S₂ and γ₂₃ denotes aninterfacial tension between the substrate S₂ and the substrate S₃.

As the cohesion between the elements of the organic film S₂ becomessmaller than the adhesion between the respective substrates S₁ and S₃and the organic film S₂, the laser transfer characteristic improves.

However, a lighting-emitting layer of the conventional organic ELdisplay device is usually made of a polymer film which has a highmolecular weight. Therefore, the cohesion between elements of thepolymer film is relatively large. Accordingly, the polymer film shows abad transfer characteristic in the conventional organic EL displaydevice.

That is, the conventional art does not disclose a technique that canimprove a transfer characteristic where the light-emitting layer isformed using the laser transfer technique.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide alight-emitting polymer composition which can improve a transfercharacteristic where a light-emitting layer of an organic EL displaydevice is formed using a laser transfer technique.

It is another object of the present invention to provide alight-emitting polymer composition which can improve a light-emittingefficiency of an organic EL display device.

Additional objects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

To achieve the above and other objects of the present invention, thereis provided a light-emitting polymer composition for a light-emittinglayer in an organic EL display, comprising at least first and secondlight-emitting polymers having elements, wherein the first and secondlight-emitting polymers have different interfacial characteristics whichlower a cohesion between the elements of the first and secondlight-emitting polymers, and a corresponding wavelength spectrum of thefirst light-emitting polymer overlaps a corresponding wavelengthspectrum of the second light-emitting polymer, so as to have an energytransfer in the light-emitting polymer composition.

The light-emitting polymer composition further includes an additivewhich improves adhesion of the light-emitting composition to a substrateand lowers the cohesion between the elements of the first and secondlight-emitting polymers. The additive is “optically inert.” That is, theaddition of the additive to the light-emitting polymer composition doesnot affect a final emitting spectrum and a color index of thelight-emitting polymer composition in a range of visible light region of400 nm to 800 nm, wherein the range is a emitting light region of thelight-emitting polymer composition.

The additive is one of an optically inert polymer, an optically inertlow-molecular material, a polymer having a carrier transporting ability,and a low-molecular material having a carrier transporting ability.

The optically inert polymer is selected from a group consisting of apolystyrene, a poly(styrene-butadione) copolymer, apolymethylmethacrylate, a polyalphamethylstyrene, astyrene-methylmethacrylate copolymer, a polybutadiene, a polycarbonate,a polyethyleneterephthalate, a polyestersulfonate, a polysulfonate, apolyarylate, a fluorinepolyimide, a transparent fluoric resin, and atransparent acrylic resin.

The polymer having the carrier transporting ability is selected from agroup consisting of an arylamine, a perylrene group and a pyrrole-basedpolymer. The low-molecular material having the carrier transportingability is, for example, an arylamine, a hydrazone, a carbazole, astylbene, a staburst group, and an oxadiazole. A mixing mass ratio ofthe first light-emitting polymer is in a range between 0.3 and 0.8, anda mixing mass ratio of the second light-emitting polymer is in a rangebetween 0.2 and 0.7. A mixing mass ratio of the additive is less than0.7.

To achieve the above and other objects according to another aspect ofthe present invention, there is provided a light-emitting polymercomposition for a light-emitting layer of an organic EL display,comprising a light-emitting polymer having elements and an additivewhich improves adhesion of the light-emitting composition to a substrateof the organic EL display, and lowers a cohesion between the elements ofthe light-emitting polymers.

The additive is one of an optically inert polymer, an optically inertlow-molecular material, a polymer having a carrier transporting ability,and a low-molecular material having a carrier transporting ability.

The optically inert polymer is selected from a group consisting of apolystyrene, a poly(styrene-butadione) copolymer, apolymethylmethacrylate, a polyalphamethylstyrene, astyrene-methylmethacrylate copolymer, a polybutadiene, a polycarbonate,a polyethyleneterephthalate, a polyestersulfonate, a polysulfonate, apolyarylate, a fluorinepolyimide, a transparent fluoric resin, and atransparent acrylic resin.

The polymer having the carrier transporting ability is selected from agroup consisting of an arylamine, a perylrene group and a pyrrole-basedpolymer. The low-molecular material having the carrier transportingability is, for example, an arylamine, a hydrazone, a carbazole, astylbene, a staburst group, and an oxadiazole. A mixing mass ratio ofthe additive is in a range between 0.375 and 0.667.

To achieve the above and other objects according to yet another aspectof the present invention, there is provided an organic EL display devicecomprising an anode, a hole transporting layer formed on the anode, alight-emitting layer comprising a light-emitting polymer compositionincluding at least first and second light-emitting polymers havingelements, wherein the first and second light-emitting polymers havedifferent interfacial characteristics which lower a cohesion between theelements of the first and second light-emitting polymers, and a cathodeformed on the light-emitting layer.

A corresponding wavelength spectrum of the first light-emitting polymeroverlaps a corresponding wavelength spectrum of the secondlight-emitting polymer so as to have an energy transfer in thelight-emitting polymer composition.

The light-emitting polymer composition further comprises an additivewhich improves adhesion of the light-emitting composition to a substrateof the organic display device, and lowers the cohesion between theelements of the first and second light-emitting polymers.

To achieve the above and other objects according to still another aspectof the present invention, there is provided an organic EL display devicecomprising an anode, a hole transporting layer formed on the anode, alight-emitting layer comprising a light-emitting polymer compositionincluding a light-emitting polymer having elements, and an additivewhich improves adhesion of the light-emitting composition to a substrateand lowers a cohesion between the elements of the light-emittingpolymer, and a cathode formed on the light-emitting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome apparent and more readily appreciated from the followingdescription of the embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a schematic view illustrating a laser transfer operation forpatterning a light-emitting layer of a conventional organic EL displaydevice;

FIG. 2 is a cross-sectional view illustrating an organic EL displaydevice according to an embodiment of the present invention;

FIG. 3 is a mixing mass ratio graph showing a mixing mass ratio of alight-emitting polymer composition according to the present invention;

FIG. 4 is a graph illustrating a wavelength spectrum of the organic ELdisplay device of FIG. 2 having a light-emitting polymer composition ofthe present invention;

FIG. 5 is a graph illustrating a wavelength spectrum of the organic ELdisplay device of FIG. 2 according to variations of a mixing mass ratioof the light-emitting polymer composition;

FIG. 6 is a CIE color coordinate of the organic EL display device havinga mixing mass ratio of SUPER YELLOW:RED-B:polystyrene=0.64:0.28:0.08,respectively, according to the present invention; and

FIG. 7 is a wavelength spectrum of the organic EL display device of FIG.6 having the light-emitting polymer composition of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

A transfer characteristic of a polymer film can be improved by loweringa cohesion between elements of the polymer film and/or raising anadhesion between a substrate and the polymer film.

A light-emitting polymer composition according to an embodiment of thepresent invention includes at least two kinds of light-emitting polymershaving different interfacial properties.

Two kinds of light-emitting polymers having different interfacialproperties are mixed to prepare a polymer film. When a laser beam isirradiated to the polymer film, a phase separation occurs. The polymerfilm begins to transfer to a substrate from a portion of the polymerfilm in which the phase separation occurs. The phase separation lowers acohesion between elements of the polymer film without greatly loweringan adhesion between the substrate and the polymer film. Consequently, atransfer characteristic of the polymer film can be improved. As thepolymers have a greater difference in interfacial characteristic, thepolymer film is transferred more efficiently.

However, when the two kinds of polymers are mixed, a light-emittingefficiency of an organic EL display device may be lowered. Therefore,the light-emitting polymer composition of the present invention has astructure that efficiently performs an energy transfer. That is, anenergy received by one polymer (hereinafter, host polymer) ismomentarily transferred to the other polymer (hereinafter, a dopantpolymer). Therefore, wavelength spectrums of the host polymer and thedopant polymer overlap each other.

For example, a yellow light-emitting polymer, in which a wavelength ofabsorbed light is relatively small (i.e., has a relatively high energy),receives energy to emit yellow light, and a red light-emitting polymer,in which a wavelength of absorbed light is large (i.e., has a relativelylow energy), receives the energy from the yellow light-emitting polymerto finally emit red light. In other words, since the energy transferoccurs momentarily, only the wavelength spectrum of the redlight-emitting polymer is finally observed.

The light-emitting polymer composition can be prepared to emit R, G andB colors as well as a single color in the above-described method.

The light-emitting polymer composition may further include an additivewhich improves the adhesion between the polymer film and the substrate,and simultaneously lowers the cohesion between elements of the polymerfilm. The additive is “optically inert.” That is, the addition of theadditive to the light-emitting polymer composition does not affect afinal emitting spectrum and a color index of the light-emitting polymercomposition in a range of visible light region of 400 nm to 800 nm,wherein the range is a emitting light region of the light-emittingpolymer composition.

The additive includes an optically inert polymer, an optically inertlow-molecular material, a polymer having a carrier transporting ability,or a low-molecular material having a carrier transporting ability.

The optically inert polymer includes a polystyrene, apoly(styrene-butadione)copolymer, a polymethylmethacrylate, apolyalphamethylstyrene, a styrene-methylmethacrylate copolymer, apolybutadiene, a polycarbonate, a polyethyleneterephthalate, apolyestersulfonate, a polysulfonate, a polyarylate, a fluorinepolyimide,a transparent fluoric resin, and a transparent acrylic resin. Thepolymer having the carrier transporting ability includes an arylamine, aperylrene group and a pyrrole-based polymer. The low-molecular materialhaving a carrier transporting ability includes one of an arylamine, ahydrazone, a carbazole, a stylbene, a staburst group, and an oxadiazole.

A mixing mass ratio of the two kinds of light-emitting polymers of thelight-emitting polymer composition is as follows: 0.3<first polymer<0.8;and 0.2<second polymer<0.7. A mixing mass ratio of the additive is lessthan 0.7.

A light-emitting polymer composition according to another embodiment ofthe present invention can include one kind of polymer and an additive.The additive is one of the above-described additives. In this case,since the energy transfer does not occur, a light-emitting efficiency isnot improved, but the adhesion between a substrate and a polymer filmprepared using the light-emitting polymer composition is improved. Alarge amount of the additive may reduce the light-emitting efficiency.Accordingly, a mixing mass ratio of the additive in this case is in arange between 0.375 and 0.667.

The mixing mass ratios depend on pattern characteristics and a colorpurity of a resulting device.

A method of manufacturing an organic EL display device according to thepresent invention is described below.

A substrate having an anode is cleaned in, for example, an acetone andan isopropylalcohol in sequence and is UV/ozone-treated. A holetransporting layer is, for example, spin-coated on the substrate andthen baked. A light-emitting polymer composition of the presentinvention is deposited on a transfer substrate to tens of nanometers(nm) to thereby form a transfer film. A light-emitting layer having R, Gand B color patterns is patterned on the hole transporting layer byusing a laser transfer technique. A cathode is formed on thelight-emitting layer. Finally, an encapsulating process is performed tocomplete the organic EL display device.

The organic EL display device of the present invention has an excellenttransfer characteristic, thereby forming the light-emitting layer havingan edge roughness of less than 5 μm.

FIG. 2 shows a cross-sectional view illustrating an organic EL displaydevice according to the present invention. In FIG. 2, reference numerals100, 200, 300 and 400 denote a cathode, a light-emitting layer, a holetransporting layer, and an anode, respectively.

Example 1 below describes a light-emitting polymer composition havingtwo kinds of light-emitting polymers and an additive, and an organic ELdisplay device using the same according to the present invention:

Example 1

The two kinds of light-emitting polymers and the additive are mixed inan appropriate mass ratio and dissolved in a single solvent to preparethe light-emitting polymer composition. One light-emitting polymer is aPPV-based yellow electrolight-emitting polymer available under the tradename “SUPER YELLOW” from Covion Organic Semiconductors GmbH. The otherlight-emitting polymer is a PFO-based red electrolight-emitting polymeravailable under the trade name “RED-B” from Dow Chemical Company. Theadditive is a polystyrene having a molecular weight of 2,500 availablefrom Sigma-Aldrich Corporation.

The light-emitting polymer composition is sufficiently stirred at atemperature of 60° C. for at least three hours. The light-emittingpolymer composition is deposited on a transfer substrate to a thickness80 nm to thereby form a transfer film. A substrate having an anodeelectrode pattern is cleaned and then UV/ozone-treated. A holetransporting layer made of a “PEDOT/PSS” from Bayer AG is coated on thesubstrate to a thickness of 50 nm. The transfer film undergoes a lasertransfer technique to thereby form a light-emitting layer of the organicEL display device. A cathode electrode including an LiF layer of 1 nmand an Al layer of 150 nm is formed on the light-emitting layer.Finally, an encapsulating process is performed to complete the organicEL display device.

A mixing mass ratio of the above light-emitting polymer compositionwhich satisfies a Commission Internationale de l'Eclairage (CIE) colorcoordinate and have an improved transfer characteristic is as follows:0.3<SUPER YELLOW<0.8, 0.2<RED-B<0.7, and polystyrene<0.7.

One of the optimum mixing mass ratio of the above light-emitting polymercomposition is as follows: SUPERYELLOW:RED-B:polystyrene=0.64:0.28:0.08. In this case, a light-emittingefficiency is 1.25 cd/A, and a color coordinate is x=0.66 and y=0.33(CIE1931, 300 Cd/m² at a voltage of 6.5 volts).

In the above light-emitting polymer composition, where the organic ELdisplay device emits a red light, which is a finally observed light,SUPER YELLOW is a host polymer and RED-B is a dopant polymer.

FIG. 3 shows a mixing mass ratio graph of a light-emitting polymercomposition of the present invention which satisfies a CIE colorcoordinate and have an improved transfer characteristic. A non-dottedregion (a region not filled with dots) is a feasible region that cansatisfy the CIE coordinate and has the laser transfer characteristic.

FIG. 4 shows a graph illustrating a wavelength spectrum of an organic ELdisplay device according to the present invention. As shown in FIG. 4, awavelength spectrum of emitted light overlaps a wavelength spectrum ofabsorbed light in a wavelength range between 500 nm and 700 nm.Therefore, an energy transfer from i.e., SUPER YELLOW to RED-B occursmomentarily, so that only a wavelength spectrum of red light isobserved.

FIG. 5 shows a graph illustrating a wavelength spectrum of an organic ELdisplay device of the present invention according to variations of amixing mass ratio of a light-emitting polymer composition used in theorganic EL display device. As shown in FIG. 5, a wavelength spectrum ofan organic EL display device having a mixing mass ratio of RED-B of 25%is almost identical to that of where a mixing mass ratio of RED-B is100%.

FIGS. 6 and 7 show a CIE color coordinate and a wavelength spectrum ofan organic EL display device having a light-emitting polymer compositionwith a mixing mass ratio of SUPERYELLOW:RED-B:polystyrene=0.64:0.28:0.08, respectively.

Example 2 below describes a light-emitting polymer composition havingone light-emitting polymer and an additive, and an organic EL displaydevice using the same according to the present invention.

Example 2

The light-emitting polymer is a red electrolight-emitting polymeravailable under the trade name “AEF 2009 & 2045” from Covion OrganicSemiconductors GmbH. The additive is a polystyrene available fromSigma-Aldrich Corporation. The molecular weight of the polystyrene is ina range between 2,000 and 2,500. The closer the molecular weight of thepolystyrene is to 2,000, better the edge roughness of the light-emittinglayer.

The light-emitting polymer and the additive are mixed in an appropriatemixing mass ratio and dissolved in a toluene to prepare thelight-emitting polymer composition.

The light-emitting polymer composition is sufficiently stirred at atemperature of 60° C. for at least three hours. The light-emittingpolymer composition is deposited on a transfer substrate to a thickness80 nm to thereby form a transfer film. A substrate having an anode iscleaned and then UV/ozone-treated for fifteen minutes. A holetransporting layer made of “PEDOT/PSS” from Bayer AG is coated on thesubstrate to a thickness of 50 nm. The transfer film undergoes a lasertransfer technique to thereby form a light-emitting layer of the organicEL display device. A cathode electrode is formed on the light-emittinglayer. Finally, an encapsulating process is performed to complete theorganic EL display device.

The mixing mass ratio of the light-emitting polymer composition is asfollows: 0.333<AEF 2009 or 2045<0.675, and 0.375<polystyrene<0.667. Thelight-emitting layer has an edge roughness of less than 5 μm.

Tables 1 and 2 below show the light emitting efficiency and the CIEcolor coordinate of the organic EL display device manufactured in theabove-described condition.

An organic EL display device of Table 1 has the following structure:substrate having anode/hole transporting layer of 50nm/AEF2009:polystyrene(1:1)/cathode having a Ca layer of 30 nm and an Aglayer of 250 nm.

TABLE 1 Spincoating Turn-on Voltage (V) Efficiency speed Thicknessvoltage at 100 at 100 CIE (1931) (rpm) (Å) (V) Cd/ Cd/ X Y CR/PS 2000800 4.5 7.5 0.78 0.6601 0.3383 (#1) CR/PS 2000 800 4.0 7.0 0.83 0.66280.3354 (#2) CR/PS 2000 800 4.0 6.5 0.77 0.6605 0.3376 (#3)

An organic EL display device of Table 2 has the following structure:substrate having anode/hole transporting of 50nm/AEF2045:polystyrene(1:2)/cathode having a Ca layer of 30 nm and a Aglayer of 250 nm.

TABLE 2 Voltage Turn-on (V) Efficiency Thickness voltage at 100 at 100CIE (1931) (Å) (V) Cd/ Cd/ x Y CR/PS 700 3.5 5.5 0.79 0.6658 0.3342 (#1)CR/PS 800 3.5 6.0 1.34 0.6682 0.3309 (#2) CR/PS 850 3.5 6.5 1.22 0.66820.3309 (#3) CR/PS 900 4.0 7.0 0.51 0.6675 0.3316 (#4)

According to the present invention, a transfer characteristic of alight-emitting layer of an organic EL display device, formed using alaser transfer technique, is improved. Accordingly, a resulting patternof the light-emitting layer is improved. In addition, the organic ELdisplay device of the present invention shows an improved light-emittingefficiency, as compared to a conventional, i.e., pure red light-emittingpolymer in the same luminance condition.

Although a few embodiments of the present invention have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

1. A donor substrate for Laser Induced Thermal Imaging (LITI) method,comprising: a base substrate; a light-to-heat conversion layer formed onthe base substrate; and a transferring layer formed on the light-to-heatconversion layer, wherein, the transferring layer comprises: first andsecond light-emitting polymers having chemical elements forming alight-emitting polymer composition, and an additive which improvesadhesion of the light-emitting composition to the base substrate andlowers the cohesion between the chemical elements of the first andsecond light-emitting polymers, wherein the first and secondlight-emitting polymers have different interfacial characteristics whichlower a cohesion between the chemical elements of the first and secondlight-emitting polymers, and wherein a corresponding wavelength spectrumof the first light-emitting polymer overlaps a corresponding wavelengthspectrum of the second light-emitting polymer in a wavelength rangebetween 500 nm and 700 nm, so as to allow an energy transfer in thelight-emitting polymer composition, and wherein the first light-emittingpolymer has a mixing mass ratio in a range between 0.3 and 0.8, thesecond light-emitting polymer has a mixing mass ratio in a range between0.2 and 0.7, and the additive has a mixing mass ratio of less than 0.7.2. The donor substrate of claim 1, wherein the additive is one of anoptically inert polymer, an optically inert low-molecular material, apolymer having a carrier transporting ability, and a low-molecularmaterial having a carrier transporting ability.
 3. The donor substrateof claim 2, wherein the optically inert polymer is selected from a groupconsisting of a polystyrene, a poly(styrene-butadione) copolymer, apolymethylmethacrylate, a polyalphamethylstyrene, astyrene-methylmethacrylate copolymer, a polybutadiene, a polycarbonate,a polyethylene terephthalate, a polyester sulfonate, a polysulfonate, apolyarylate, a fluorine polyimide, a transparent fluoric resin, and atransparent acrylic resin.
 4. The donor substrate of claim 2, whereinthe polymer having the carrier transporting ability is selected from agroup consisting of an arylamine based polymer, a perylene group basedpolymer and a pyrrole-based polymer.
 5. The donor substrate of claim 2,wherein the low-molecular material having the carrier transportingability is one of an arylamine, a hydrazone, a carbazole, a stilbene, astarburst group, and an oxadiazole.
 6. A donor substrate for LaserInduced Thermal Imaging (LITI) method, comprising: a base substrate; alight-to-heat conversion layer on the base substrate; and a transferringlayer on the light-to-heat conversion layer, wherein the transferringlayer comprises a light-emitting polymer composition having first andsecond light-emitting polymers; and an additive which improves adhesionof the light-emitting polymer composition to the base substrate andlowers a cohesion between chemical elements of the light-emittingpolymer composition, wherein the additive is one of an optically inertpolymer, an optically inert low-molecular material, a polymer having acarrier transporting ability, and a low-molecular material having acarrier transporting ability, wherein the light-emitting polymercomposition has a mixing mass ratio in a range between 0.333 and 0.675,and the additive has a mixing mass ratio in a range between 0.375 and0.667, and wherein a wavelength spectrum of the first light-emittingpolymer overlaps a corresponding wavelength spectrum of the secondlight-emitting polymer in a wavelength range between 500 nm and 700 nm,so as to allow an energy transfer in the light-emitting polymercomposition.
 7. The donor substrate of claim 6, wherein the opticallyinert polymer is selected from a group consisting of a polystyrene, apoly(styrene-butadione) copolymer, a polymethylmethacrylate, apolyalphamethylstyrene, a styrene-methylmethacrylate copolymer, apolybutadiene, a polycarbonate, a polyethylene terephthalate, apolyester sulfonate, a polysulfonate, a polyarylate, a fluorinepolyimide, a transparent fluoric resin, and a transparent acrylic resin.8. The donor substrate of claim 6, wherein the polymer having thecarrier transporting ability is selected from a group consisting of anarylamine based polymer, a perylene group based polymer and apyrrole-based polymer.
 9. The donor substrate of claim 6, wherein thelow-molecular material having the carrier transporting ability is one ofan arylamine, a hydrazone, a carbazole, a stilbene, a starburst group,and an oxadiazole.
 10. A donor substrate for Laser Induced ThermalImaging (LITI) method, comprising: a base substrate; a light-to-heatconversion layer on the base substrate; and a transferring layer on thelight-to-heat conversion layer, wherein the transferring layer comprisesfirst and second light-emitting polymers forming a light-emittingcomposition which have different interfacial characteristics that lowera cohesion between elements of the light-emitting polymers, and whereina wavelength spectrum of emitted light of one of the light-emittingpolymers overlaps a wavelength spectrum of absorbed light of another oneof the light-emitting polymers in a wavelength range between 500 nm and700 nm, and wherein the first light-emitting polymer has a mixing massratio in a range between 0.3 and 0.8, and the second light-emittingpolymer has a mixing mass ratio in a range between 0.2 and 0.7.
 11. Thedonor substrate of claim 10, wherein the transferring layer furthercomprises an additive which improves adhesion of the light-emittingcomposition to the base substrate and lowers the cohesion between theelements of the light-emitting polymers.
 12. A donor substrate for LaserInduced Thermal Imaging (LITI) method, comprising: a base substrate; alight-to-heat conversion layer formed on the base substrate; and alight-emitting polymer composition formed on the light-to-heatconversion layer, wherein, the light-emitting polymer compositioncomprises: a host polymer and a dopant polymer having chemical elements,and an additive, the host polymer having a mixing mass ratio in a rangebetween 0.3 and 0.8, the dopant polymer having a mixing mass ratio in arange between 0.2 and 0.7, and the additive having a mixing mass ratioof less than 0.7, wherein the host and dopant polymers have differentinterfacial characteristics which lower a cohesion between the chemicalelements of the host and dopant polymers, and wherein a correspondingwavelength spectrum of the host polymer overlaps a correspondingwavelength spectrum of the dopant polymer in a wavelength range between500 nm and 700 nm, so that energy received by the host polymer ismomentarily transferred to the dopant polymer.